The dynamic aspects of sound-- the amplitude and frequency changes that occur over time- are crucial information- bearing elements of auditory perception and communication. The ability of the auditory system to follow and to resolve such changes is the topic of this proposal. The proposed project is a comprehensive behavioral study, using normal-hearing adults, of the ability to extract information from changes in the amplitude and the spectrum of sound. The proposal consists of three related projects that investigate increasingly complex aspects of dynamic auditory processing. The first project addresses basic issues in auditory coding. One focus is on how normal human hearing can operate over a huge intensity range. The proposed experiments address hypotheses based on physiological data that suggest a possible role for suppression, cochlear efferents, and nonlinear spread of excitation. The other focus is on the role of fine-structure information in monaural hearing. The proposed experiments on this basic, long-standing issue will delineate the relative importance of fine-structure and envelope information in detection and discrimination. The second project examines the ability of the auditory system to extract information from dynamic changes in amplitude such as produced by amplitude and frequency modulation. The general aim of this project is to develop a comprehensive empirical and theoretical account of such processing, including delineation of those aspects of the amplitude envelope that are important for detection and discrimination. The third project, on supra-threshold dynamic processing, is concerned with the processing of amplitude changes that are highly detectable and, as such, represents a significant extension of previous research. The hypotheses driving the specific research questions are based upon data and theory from threshold phenomenon. The general aim of this project is to extend our understanding of dynamic processing to more realistic auditory stimuli. Overall, these projects will provide information of fundamental importance for understanding the basic properties of normal human hearing and, eventually, for understanding the perceptual consequences of hearing impairment. It will help provide a bridge between auditory physiology and real-world hearing. This is essential for a full understanding of hearing and for the development and evaluation of strategies for alleviating hearing loss.